Neutralization of crude dry-cleaning soaps



U i d S ews. aten '0 George W. Ayers, Chicago, Ill., assignor to The Pure Oil Company, Chicago, 111., a corporation of Ohio Application September 7, 1955 Serial No. 533,004

1 Claim. (Cl. 252-161) No Drawing.

The present invention relates to a process for preparing substantially neutral soaps or their neutral components suitable for use in dry-cleaning. More particularly, the present invention is directed to a novel process for substantially neutralizing slightly alkaline petroleum sulfonates.

Petroleum sulfonic acids are usually derived from the treatment of lubricating oil distillates with fuming sulfuric acid in the manufacture of white oils and other oils. The acid treatment yields an acid sludge which is oil-insoluble and which contains water-soluble green sulfonic acids. The oil remaining from the acid treatment contains higher molecular weight, oil-soluble mahogany sulfo'nic acids. The oil-soluble petroleum sulfonic acids average about 30 carbon atoms in length and have average molecular weights of about 350-500. They are believed to be reaction products of long chain alkyl substituted aromatic hydrocarbons, having either one or two aromatic rings per molecule, in which the sulfonate radical is attached to the aromatic ring nucleus. These sulfonic acids are usually approximately neutralized with caustic soda and then extracted with aqueous alcohol solution or similar extracting medium. Distillation of the alcohol solution yields the concentrated sodium mahogany sulfonates as a distillation residue in substantially anhydrous form. They may then be converted to alkaline earth metal salts for use as motor oil detergents, or be put to a variety of other uses in the alkali metal salt form,including use as soaps in the dry-cleaning industry.

In the dry-cleaning industry, garments are ordinarily cleaned with Stoddard solvent or other hydrocarbon solvents such as V.M. and P. naphtha or 140 Solvent. The dry-cleaning solvent contains up to about 4% of a dry-cleaning soap, which in turn is usually composed of, at least in part as indicated above, sodium mahogany sulfonates. As above-mentioned, during the original preparation and separation of the mahogany sulfonates the reaction between the basic reagent, usually sodium hydroxide, and the oil-soluble sulfonic acids is ordinarily carried out on a quantity scale and slight overneutralization actually occurs in most cases; The alkalinity of these crude mahogany sultonates commonly is not reduced to the point where they are harmless to all dyed garments or fabrics.

When the slightly alkaline mahogany sulfonates are to be used in the dry-cleaning industry, they must be subjected to a time-consuming, expensive, careful adjustment of the alkalinity. The tedious neutralization is ordinarily carried out by means of a strong acid with careful laboratory control by titration utilizing a color indicator. lizing aqueous reagents. After the neutralization, if the initially substantially anhydrous sulfonate solution contains an appreciable quantity of water, it is subjected to a further expensive water-removal step to obtain substantially anhydrous mahogany sulfonate mixtures, this substantially anhydrous form being necessary when the Moreover, the neutralization takes place uti- Patented Jan, 1 3, p 1960 sulfonates are to be added to dry-cleaning naphtha and also in certain other applications. Presence of an appreciable amount of water in the naphtha tends to wrin-.

kle the cloth and to shrink the fibers in contact with it, and hence is very undesirable.

Whether the two-bath or the one-bath system is used in dry-cleaning garments with soap-containing naphtha, some of the naphtha evaporates from the garments during wringing and tumbling, leaving a film of the soap deposited on the garments. This is desirable because the adsorbed soap confers softness and good appearance to the dry-cleaned garment. It is essential that the soap used in dry-cleaning be substantially neutral in reaction, because mineral acids or the stronger organic acids and bases may weaken the fibers or change the color shade, particularly with red-, purple-, and blue-colored garments. Commercial mahogany sulfonates, owing to the necessity of adjusting their alkalinity substantially to the neutral point and to the expense of the usual means of doing so, have rarely been utilized as such'in the dry-cleaning industry other than as components of the much used, privately branded dry-cleaning soaps.

I have now unexpectedly found a method for effectively neutralizing commercial, slightly alkaline, mahogany -sulfonates and rendering them eminently suitable for use as dry-cleaning soaps and also for use in other applications requiring neutral mixtures of mahogany sulfonate soaps.

Accordingly, it is an object of my invention to provide substantially neutral mahogany sulfonate mixtures in an inexpensive and simple manner.

It is also an object of my invention to provide a substantially anhydrous method of neutralizing an alkaline soap or-mixture of soaps of petroleum-derived organic acids.

It is another object of my invention to provide a substantially anhydrous method of neutralizing an alkaline mixture of mahogany sulfonates.

It is a further object of my invention to provide a simple, quick and inexpensive process for adjusting the alkalinity of a mahogany sulfonate mixture to approximate neutrality without introducing water into the mixture and without over-neutralizing.

In general, my invention resides in the adjustment of the alkalinity of a soap or mixture of soaps of petroleumderived acids to approximate neutrality by'the use of substantially anhydrous carbon dioxide.

More particularly, my invention covers the neutraliza-v tion of slightly alkaline mahogany sulfonate soaps by themselves or in situ in naphtha by introducing substantially anhydrous carbon dioxide.

In myprocess, the material to be neutralized is oil: soluble mahogany sulfonate soap or a mixture of two or more of said soaps. The soaps are the oil-soluble alkali metal or quaternary ammonium salts of oil-soluble petroleum sulfonic acids and are prepared as abovedescribed. Specific examples are as follows: potassium mahogany sulfonate, sodium mahogany sulfonate, lithium mahogany sulfonate and trimethylbenzylammonium petroleum sulfonate. My invention also contemplates the use of other petroleum-derived soaps, that is, for example, the oil-soluble soaps of naphthenic acids of various molecular weights, such as sodium naphthenate, potassium naphthenate, lithium naphthenate and quaternary ammonium naphthenates. The soaps may be treated in a separate, substantially anhydrous mixture or solution, or may be already present in substantially anhydrous form in naphtha or other base oil or substantion takes place.

The soap or soap mixture in a suitable reaction vessel, such as, for example, a 100 gallon metal drum, is subjected to substantially anhydrous carbon dioxide-containing gas. Carbon dioxide as the sole gas is preferred, although. there also may be present other gases which do not enter into reaction under the treatment conditions with the soaps to be neutralized or other matter present. Thus, nitrogen, for example, may be present as a diluent for the carbon dioxide. The soap or soap mixture is preferably subjected to agitation, such as by a mechanical.

' stirrer, during the reaction period in order to facilitate intimate contacting of the carbon dioxide wtih all portions of the soap mixture. The temperature during the reaction period may be up to 300 F. or more at normal atmospheric pressure, preferably about 702 F. Temperatures above about 300 'F. may produce products in thesulfonate mixture which detract from its detergency or'which impart odor to the product.

i The concentration of the carbon dioxide in the soap mixture may vary within wide limits to suit the practical requirements for speed ofcompletion of the neutraliza tion reaction of my process. For example, 100 cc; of substantially pure carbondioxide per minute at 70 may be introduced per 100 gms; of sodium mahogany sulfonate until a withdrawn 0.1- gram portion of the soap tests neutral in the presence of 50 cc. of neutral 95% alcohol using one drop of 1% phenolphthalein solution or other properly chosen indicator.

7 The soap or soap mixture is kept in contact with the carbon dioxide until substantial neutrality is reached, as demonstrated by failure of a gram sample to give a pink color in the presence of 50 cc. of neutral 95% alcohol and one drop of 1% phenolphthalein indicator. Phenolphthalein is colorless when neutral or acid and red or pink when alkaline. The neutral point-for phenolphthalein (which isusually used in a 95% solution of ethyl alcohol) is pH 8.0. s 7

Where the soap or soap mixture is initially acidic rather than alkaline, it is obvious that a slight excess of concentrated caustic soda solution or other strong base may be added to overneutraliz e' the soap or soap mixture and render it slightly alkaline. As strong a base solution as possible is usedto minimize the introduction of water into the mixture. Optionally, the solution may be rendered substantially anhydrous. The procedure for adjustinglthe now alkaline mixture to a substantially neutralv point may then be followed as is described above for a, soap or soap mixture whichi nitially is alkaline, that is, a current of carbon dioxide-containing gas may be added to the soap or soap mixture at a temperature of up to about 300? F., preferably 70-2 00 F. Excess carbon dioxide added to. the mixture after neutrality has 7 been reached will not affect the neutralization,that. is,

will not render the mixture sufficiently acidic so that it liable to change the shades of certain dyes,. but will escape from the mixture in gaseous forrnp- The'dangerof passing beyond the neutral point and having to readjust the mixture to the neutral point in the substantiallynonaqueous environment is thus eliminated.

It should be pointed out that whilethe exact mechanism of reaction between the carbon dioxide and the soap or soap mixture is not definitely known, the in stant process is equally effective whether the soap or soap mixture appears alone or has already'been added to the naphtha or other dry cleaning agent. 7 The following examples further illustrate the basic precepts of my invention:

Example 1 -A mixture of sodium mahogany sulfonates prepared from a Mid-Continent lubricating oil distillate by'treatment with fuming sulfuric acid, separation of the sludge, treatment of the oil-sulfonic acid product with caustic soda and partial dehydration, had the following character- 'istics':

pH value when tested in presence of water (1 cc. of sample in 100 cc. distilled .fonate and possible damage to dyed fabrics.

of mixture.

The alkalinity of this sulfonate mixture, which is harmful to certain dyed fabrics, is reduced by the addition in an open kettle of 1 liter of substantially pure gaseous carbon dioxide per 1000 grams mahogany sulfonate mixture per minute. The. treatment is carried out at 70 F. and allowed to continue for approximately 5 minutes, after which time a 0.1 g. sample of the soap mixture in 50 cc. of neutral alcohol is tested with one drop of 1% phenolphthalein indicator solution. The resulting mixture is colorless, indicating that a product harmless to' dyed fabrics has been attained. The stream of carbon dioxide gas, entering the open reaction vessel at a point near the bottom and bubbling up through the soap mixture, which is under constant mechanical agitation, is therefore discontinued. Any excess carbon dioxide escapes in bubbles from the surface of the soap mixture while the mixture is heated to 150 F. The soap mixture is then added to a substantially anhydrous Stoddard Solvent in approximately 2% amount to prepare a final product suitable for use in dry cleaning of cloth.

Example II value (when 1 cc. is added to if cc. of distilled water) 9. Average mol. weight 340.. Concentration of water Less than 0.5%.

To 1 liter of the sulfonate-containing Stoddard Solvent inan open-mouthvcssel is added, by bubbling therethrough while the solution is under agitation with a rotary stirrer, substantially pure gaseous carbon dioxide at a flow rate of approximately 1 liter per hr. After about 20 minutes, a 50 cc. sample of the solution is removed, added to 50 cc. of neutral 95% alcohol, and one drop of 1% phenolphthalein indicator solution is added. The solution remains colorless, indicating thatthe solution is safe for the cleaning offabrics, particularly-dyed fabrics. Immersion of pieces of blue, red and purple dyed cloth in this naphtha sol'utionof. sodium mahogany sulfonate caused no change in shade'of the dyed piecesof cloth. Carbon dioxide, unl ike.iacids such as -sulfuric and hydrochloric acid, and certain organic acids" such as formicacid, is unique in' its action because no thought has to be given to overneutralization ofthei crude sodium mahogany sul- It is to be noted that the presence of naphtha inno way affects the reaction. between the carbon dioxide and the alkaline constituents. Y

The above. examples. clearly show that substantial neutralization of a soap. or soap mixture comprising oilsoluble mahogany sulfonate can be achieved simply, quickly andinexpensively bythe process of my invention andin a substantially anhydrousenvironment. After the neutralization step, the initially alkaline soap mixture is ready for use without further treatment, that is, water neednot be removed therefrom. If all particles of sludge have notbeen completely separated from the sodium mahogany sulfon'ate, itmay be necessary to filter the sodium mahogany sulfonate or its naphtha solution through diatomaceous'earth or other suitable material. The new tralization reaction, moreover, may be brought about in the cleaning agent, such as naphtha and the like, without fear of contaminating the naphtha in any way. The solutions produced are completely harmless to fabrics.

Such modifications of my process and the equipment for carrying it out as are within the skill of one versed in the art are contemplated by this invention.

1 claim and particularly point out as my invention:

A process of preparing a dry-cleaning soap which is not harmful to clothing dyes which comprises neutralizing anhydrous liquid sodium mahogany sulfonates containing traces of free alkalinity consisting solely of the same alkaline material from which the sulfonates were derived, by agitating the liquid sulfonates and continuously bubbling anhydrous carbon dioxide therethrough at a temperature of about 70 F., at a rate of one liter of carbon dioxide per minute per 1000 g. of sulfonates for a period of five minutes to produce a substantially neutral liquid as measured by a phenolphthalein indicator solution.

References Cited in the file of this patent UNITED STATES PATENTS 2,304,230 Archibald et al. Dec. 8, 1942 2,594,690 Shifiler Apr. 29, 1952 2,594,875 Condit Apr. 29, 1952 2,617,049 Assefl? et al. Nov. 4, 1952 2,715,110 Packard Aug. 9, 1955 2,760,970 LeSuer Aug. 28, T956 2,767,209 Asseff et al. Oct. 16, 1956 2,777,874 Asseff et a1. Jan. 15, 1957 OTHER REFERENCES Rudolfs Industrial Wastes, New York 1953, pp. 441- 442. 

